INTRODUCTION: Green-synthesized nanoparticles show promise as anti-biofilm and antibacterial agents in medical applications, including dental implants and oral devices. However, conventional antibacterial testing methods are laborious and lack sensitivity. Quartz tuning fork (QTF)-based biosensors offer a compelling alternative due to their high sensitivity, compact size, and cost-effectiveness. This study evaluates a QTF biosensor for quantifying the antibacterial activity of green-synthesized ZnO nanoparticles against negative and positive Gram bacteria. METHODS: The antibacterial activity of ZnO nanoparticles was tested in a simulated oral environment against  (gram-positive) and  (gram-negative) using a QTF biosensor. Changes in resonance frequency and quality factor were measured to assess bacterial growth inhibition. Experiments were conducted with varying ZnO concentrations (eg, 1 mm) to correlate sensor responses with antibacterial effects. RESULTS: The QTF biosensor detected significant antibacterial activity as resonance frequency decreased by 5.69 ± 3.81 hz () and 30.57 ± 4.01 hz () in 1 mm ZnO. Quality factor declined by 31.75 ± 7.55 for  but remained stable for . Higher bacterial concentrations (lower ZnO doses) increased damping effects, reducing the quality factor.  exhibited greater sensitivity to ZnO nanoparticles than . DISCUSSION: The QTF biosensor successfully quantified the antibacterial effects of green-synthesized ZnO nanoparticles, demonstrating its potential as a rapid, sensitive alternative to traditional methods. The differential responses of  and  suggest species-specific interactions with ZnO, warranting further study. This approach could streamline the development of biocompatible, antibacterial medical materials.